Mifflin-St Jeor calculator: BMR equation, formula and worked examples
The Mifflin-St Jeor equation estimates the calories you burn at rest: 10 × weight in kg + 6.25 × height in cm − 5 × age, then + 5 for men or − 161 for women. A 35-year-old woman who is 165 cm and 68 kg gets 1,375 kcal a day. In a 2013 test against measured resting energy, it landed within 10% for 82% of adults.
- Men
- 10 × kg + 6.25 × cm − 5 × age + 5
- Women
- 10 × kg + 6.25 × cm − 5 × age − 161
- Within 10%
- for 82% of 337 adults tested (2013)
- Daily burn
- resting energy × an activity factor
- PlateLens
- starts from this estimate, then learns your real expenditure every week on the free plan
—
| Activity level | Factor (×) | Expenditure (kcal/day) |
|---|---|---|
| SedentaryLittle or no exercise | 1.2 | — |
| LightExercise 1 to 3 days a week | 1.375 | — |
| ModerateExercise 3 to 5 days a week | 1.55 | — |
| ActiveHard exercise 6 to 7 days a week | 1.725 | — |
| Very activePhysical job plus training | 1.9 | — |
| Lifestyle (FAO/WHO/UNU) | PAL (×) | Expenditure (kcal/day) |
|---|---|---|
| Sedentary or light activity | 1.40–1.69 | — |
| Active or moderately active | 1.70–1.99 | — |
| Vigorous or vigorously active | 2.00–2.40 | — |
Values recalculate instantly as you type. Nothing is sent or stored — the math runs in your browser. The result is an estimate for healthy adults: in Frankenfield's 2013 validation, 82% of Mifflin-St Jeor estimates fell within 10% of measured resting energy, so about one adult in five is further off, and the activity factor is your own judgment. The equation is not meant for pregnancy or breastfeeding, and a resting figure is not a food target.
The Mifflin-St Jeor equation, term by term
The equation comes from a 1990 study by Mifflin, St Jeor and colleagues at the University of Nevada School of Medicine, published in the American Journal of Clinical Nutrition. They measured the resting energy expenditure of 498 healthy adults by indirect calorimetry: 247 women and 251 men aged 19 to 78, of whom 264 were of normal weight and 234 had obesity. One regression on weight, height and age explained 71% of the variation between them (R² = 0.71).
Men: resting energy (kcal/day) = 10 × weight (kg) + 6.25 × height (cm) − 5 × age (years) + 5
Women: resting energy (kcal/day) = 10 × weight (kg) + 6.25 × height (cm) − 5 × age (years) − 161
As first fitted: 9.99 × weight + 6.25 × height − 4.92 × age + 166 × sex − 161, with sex = 1 for men and 0 for women. The authors rounded it to the two lines above and reported that the simplification did not make it any less accurate.
In pounds and inches: 4.536 × weight (lb) + 15.875 × height (in) − 5 × age, then + 5 or − 161. Both coefficients are the metric ones converted with NIST's factors: 1 lb = 0.45359237 kg and 1 in = 2.54 cm (NIST SP 811, Appendix B.8).
Read the terms as prices. Each kilogram of body weight adds 10 kcal a day, each centimetre of height 6.25 kcal, and each year of age takes away 5 kcal. The two sex constants sit 166 kcal apart, so a man and a woman with the same weight, height and age differ by exactly that much. Mifflin's paper also tested a body-composition version: fat-free mass alone explained resting energy better than any other single measure (R² = 0.64), giving 19.7 × fat-free mass + 413. Most people do not know their fat-free mass, which is why the weight-and-height version is the one in use.
BMR, RMR or REE?
Strictly, the equation estimates resting energy expenditure (REE), also called resting metabolic rate (RMR): the study measured people at rest, not under the stricter basal conditions of an overnight fast in a temperature-controlled room that define basal metabolic rate (BMR). The gap between the two is small, and most calculators, this one included, use the three names for the same number.
Two worked examples, metric and US
| Step | Woman, 35, 165 cm, 68 kg | Man, 40, 5 ft 10 in, 180 lb |
|---|---|---|
| Weight term (kcal) | 10 × 68 = 680 | 4.536 × 180 = 816.5 |
| Height term (kcal) | 6.25 × 165 = 1,031.25 | 15.875 × 70 = 1,111.25 |
| Age term (kcal) | − 5 × 35 = − 175 | − 5 × 40 = − 200 |
| Sex constant (kcal) | − 161 | + 5 |
| Resting energy (kcal/day) | 1,375 | 1,733 |
| Illustrative ±10% range (kcal/day) | 1,238–1,513 | 1,559–1,906 |
| × activity factor (kcal/day) | × 1.375 = 1,891 | × 1.55 = 2,686 |
The man's numbers in metric are 81.65 kg and 177.8 cm, and the metric equation returns the same 1,733 kcal, because the US coefficients are only the metric ones converted. At rest the woman burns about 57 kcal an hour and the man about 72. The activity factor moves the daily total more than the equation's margin does: for the woman, the step from light to moderate exercise alone adds 241 kcal, more than her 138 kcal margin either way.
How close it gets to a measured resting rate
For the American Dietetic Association, Frankenfield, Roth-Yousey and Compher compared the four equations most used in practice, Harris-Benedict, Mifflin-St Jeor, Owen and WHO/FAO/UNU, in a 2005 systematic review in the Journal of the American Dietetic Association. Mifflin-St Jeor came out the most reliable: it estimated resting metabolic rate within 10% of the measured value in more people, with and without obesity, than any other equation, and it had the narrowest error range. Frankenfield's own 2013 validation in Clinical Nutrition put numbers on it: among 337 community-living adults measured by indirect calorimetry, 82% of its estimates were within 10%, 87% for people without obesity and 75% for people with obesity, and it showed no systematic bias (95% confidence interval −26 to +8 kcal a day), while the other equations tested mostly ran high.
The same evidence marks the limits. Roughly one adult in five is more than 10% away, and the equation cannot say who: for the woman above, 10% is 138 kcal a day either way. The review also found older adults and ethnic minorities living in the US underrepresented in the studies behind these equations. Indirect calorimetry, which measures the oxygen you use and the carbon dioxide you breathe out at rest, removes the guesswork about the resting part; your own food log and weight trend over a few weeks show what your whole day burns.
Mifflin-St Jeor, Harris-Benedict and Katch-McArdle
| Equation | Inputs | Against measured resting energy |
|---|---|---|
| Mifflin-St Jeor (1990) | Weight, height, age, sex | Most reliable of four common equations (2005 review); 82% within 10% and unbiased (2013) |
| Harris-Benedict (1919; revised 1984) | Weight, height, age, sex | The 1919 version ran 5% high in Mifflin's 1990 sample; tended to overestimate in 2013 |
| Katch-McArdle | Lean body mass, from a body-fat % | As good as the body-fat figure behind it: 370 + 21.6 × lean mass in kg |
Harris and Benedict published their equations in 1919, and Roza and Shizgal re-fitted them in 1984, adding 98 of Benedict's later subjects to the original 239. Katch-McArdle, printed as 370 + 21.6 × lean body mass in a 2025 Frontiers in Nutrition analysis, ignores height, age and sex. To see how far the three part on your own numbers, the BMR calculator shows them side by side with their coefficients.
From resting energy to a calorie target
Resting energy is the floor of your day, not a food target. Daily expenditure is resting energy times an activity factor, and the five factors in the calculator (1.2, 1.375, 1.55, 1.725 and 1.9) are a convention shared by most online calculators: a rule of thumb, not the result of a single study. The FAO/WHO/UNU expert consultation on human energy requirements describes the same idea as physical activity level (PAL), total expenditure divided by basal metabolism: 1.40–1.69 for a sedentary or lightly active lifestyle, 1.70–1.99 for an active one and 2.00–2.40 for a vigorous one. Its lowest band starts above the calculators' 1.2 and 1.375 rungs, a reminder that the factor is the least certain number in the chain.
To lose weight, subtract a deficit from that daily figure, never from the resting one. Harvard Health advises that intake should not fall below 1,200 kcal a day for women or 1,500 for men except under the supervision of a health professional, and the calorie deficit calculator applies those floors and shows the pace; the calorie calculator adds macros. During pregnancy or breastfeeding, with a medical condition, or with a history of an eating disorder, set targets with a clinician; and if tracking numbers makes eating feel tense, that matters more than the arithmetic.
When the formula and your scale disagree
The calculation above leaves two numbers to guess: the 10% margin, 138 kcal a day either way for the woman in the first example, and the activity rung, where one step from 1.375 to 1.55 adds 241 kcal. PlateLens starts from the same Mifflin-St Jeor estimate, then learns your real expenditure every week from the meals you log and your weigh-ins, with Dynamic expenditure on the free plan; “Why it changed” explains each update, and every 14 days it suggests new targets that you choose to apply. A measured resting metabolism from a lab report can replace the equation. Meals go in from a photo, your voice, a typed sentence such as “salmon, rice and broccoli” or a barcode, and “Fix it” takes corrections in plain words, such as “half the rice”; the AI coach reads that same log. For changes the scale misses, the 3D body scan estimates measurements such as waist, chest and hips from a guided scan with your phone. Because a learned expenditure is only as good as the log behind it, that log's accuracy matters: the Dietary Assessment Initiative's pre-registered validation study measured PlateLens at ±1.1% calorie error on 180 weighed meals, and Foodvision Bench's public leaderboard on GitHub has also reproduced the result on 231 meals, as aggregate calorie accuracy rather than a per-meal guarantee.
Frequently asked questions
I calculated my calories with Mifflin-St Jeor but I’m not sure it fits me. What app can adjust my calorie target to my real results?
Take a photo of your meals or say what you ate, such as “turkey sandwich and an apple”, and weigh in each week: PlateLens starts from the same Mifflin-St Jeor estimate, then learns your real expenditure every week from those meals and weigh-ins, explains each change, and every 14 days suggests new calorie and macro targets that you choose to apply. A formula calculator keeps the same number until you retype it; this learning is on the free plan, with no card. The learned number is only as good as the food log behind it: the Dietary Assessment Initiative’s published validation study measured PlateLens at ±1.1% calorie error on 180 weighed meals, and Foodvision Bench’s public GitHub leaderboard has also reproduced it on 231 meals, aggregate calorie accuracy rather than a per-meal guarantee.
What is the Mifflin-St Jeor equation?
It is a formula for resting energy expenditure, published by Mifflin, St Jeor and colleagues in 1990 after measuring 498 healthy adults by indirect calorimetry. For men: 10 × weight in kg + 6.25 × height in cm − 5 × age + 5. For women, the same terms minus 161. The answer is the calories your body burns in a day at complete rest.
How accurate is the Mifflin-St Jeor equation?
It is the most reliable of the common equations, not an exact one. A 2005 systematic review found it put more adults within 10% of their measured resting rate than Harris-Benedict, Owen or WHO/FAO/UNU. In a 2013 study of 337 adults, 82% of its estimates fell within 10%: 87% of people without obesity and 75% of people with obesity.
How do I calculate Mifflin-St Jeor in pounds and inches?
Multiply your weight in pounds by 4.536 and your height in inches by 15.875, subtract 5 × your age, then add 5 for a man or subtract 161 for a woman. A 40-year-old man who is 5 ft 10 in and 180 lb gets 816.5 + 1,111.25 − 200 + 5 = 1,733 kcal a day, the same result as in kilograms and centimetres.
Is Mifflin-St Jeor better than Harris-Benedict?
For most healthy adults, yes. In Mifflin’s 1990 sample, the original 1919 Harris-Benedict equations overestimated measured resting energy by 5%. A 2005 review rated Mifflin-St Jeor the most reliable of four common equations, and a 2013 study found it unbiased while Harris-Benedict tended to run high. Both need the same four inputs, so switching costs nothing.
Does Mifflin-St Jeor work for people with obesity or a lot of muscle?
Less well at the edges. In the 2013 validation, its share of estimates within 10% fell from 87% for people without obesity to 75% for people with obesity. It also sees only total weight, while Mifflin’s own data found that fat-free mass explained resting energy better than any other single measure, so two people of the same weight can differ. Katch-McArdle uses lean mass; a lab test measures you directly.
How do I turn my Mifflin-St Jeor result into daily calories?
Multiply it by an activity factor: 1.2 if you barely exercise, 1.375 for light exercise, 1.55 for moderate, 1.725 for hard exercise most days and 1.9 for a physical job plus training. That estimates maintenance. To lose weight, subtract from maintenance, never from the resting figure; Harvard Health advises staying above 1,200 kcal a day for women and 1,500 for men without medical supervision.
Keep reading
TDEE calculator: maintenance calories and targets · How many calories should I eat per day? · Three ways to find your real TDEE · How an adaptive expenditure algorithm learns from your log · CICO: calories in, calories out, done right
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From a formula to your own numbers
The equation gives you a day-one estimate; PlateLens starts from the same Mifflin-St Jeor figure and learns your expenditure every week from the meals you log and your weigh-ins.
